Last month, I linked to the above video and wondered how this beer dispenser could work. My guess was that the dispenser pushed open a perforated hole in the bottom. Now we have a confirmed explanation:

The cup features a small hole at the bottom, covered up by a circular magnet. Pressurized beer lifts the magnet up, filling the cup until the weight of the beer on top of the magnet pushes it back down, sealing the bottom. This system is not only faster (serving 56 draft beers in a minute), but minimizes spilling, to the joy of sticky-footed concert-goers everywhere.

Josh Springer, head of GrinOn, was originally developing a pitcher with a latch on the bottom, but when it turned out that would cost $30,000 to develop, he switched his focus. The GrinOn cups cost only 30 cents more than normal disposable cups, and the magnets also serve as an advertising device for drunken buffoons, who steal them to put on their refrigerators. Selling that space to advertisers generates extra revenue.